The original batch of F2A's were sent to the Navy in June 1939. After receiving a small number of planes out of 54, the reamining 44 were immediately rejected and sold to Finland. These aircraft remained in service until 1944, equipping squadrons No. 24 and No.26.
This original batch had only a 950hp Wright XR-1820-22 Cyclone radial.
Now, consider that the following
P40B: Engine: Allison V-1710-33 (-33?) - 1090hp
Brewster: Engine: Wright Cyclone XR-1820-22 - 950hp
P40B: Normal loaded weight: 7,352 lbs. (AH2 stats page)
Brewster: F2A-3 max takeoff: 7,159lbs. (closest version I could find, subtract a few hundred lbs for armor to get an idea of weight)
P40B: Fuselage type: low-drag, inline engine, streamlined fuselage
Brewster: Fuselage type: high-drag, blunt radial engine, bulky fuselage
P40B: Wing area: 236 sq ft.
Brewster: Wing area: 208.9 sq ft.
I conclude:
P40B: lower drag, higher power, larger wing area, about equal weight.
Brewster: higher drad, lower power, lesser wing area, about equal weight.
Thus, once again proving the Brewster was not the best thing there was. Turning is dependent on many things, but 2 very important things in determining rate of turn include surplus power and wing size. The P40B, bad as it is in AH, actually beats the Brewster in these two areas.
Compared to the FM2,
Engine: P&W R-1830-86 Twin Wasp -- 1,200hp
Max Takeoff: 8,762lbs.
Fuselage type: semi-streamlined radial
Wing area: 260 sq ft.
So the FM-2 has more wing area, more horsepower, and less drag than the Brewster. Hell, it has more wing area and more horsepower than the P-40B!!!! It's a bit draggier than the P40B, being a radial engine, but the cowling is more streamlined than the Brewster's, as is the tail of the fuselage (just by eyeballing it). It is about 1000 lbs heavier, but this does not handicap it much, it seems.
It seems to me that the P40B is a better replacement for the Brewster than the FM-2 is. The P40B is still better than the Brewster, and the FM-2 is ever still better than the P40B.
In WW2 Finland it was the pilots, the targets, and the situations that gave this plane a high kill ratio. It wasn't its performance.
We don't need to sub the FM-2 for brewster because it's far far better than the brewster ever was.
I thought about this while fighting Yeager in his P40B, and then did some stats checking on various planes.